Soil Ecology Restoration Group

last update July 5, 2000

REVEGETATION PROJECT AT MARINE CORPS AIR GROUND COMBAT CENTER AT 29 PALMS, CALIFORNIA


  

ABSTRACT

This is the final report for the Plant Community Restoration project at Twenty-nine Palms Marine Corps Air Ground Combat Center (MCAGCC) near Twenty-nine Palms, California. The project, which began in early 1995, was initiated by the National Resources and Environmental Affairs Directorate (NREA) at the MCAGCC as an effort to develop and test methods of native plant revegetation in disturbed areas while simultaneously controlling erosion and dust. The first effort was undertaken from February 1995 through June 1996 and involved the testing of restoration methods and procedures at the Vertical Short Takeoff and Landing site located in the Sand Hill region of the Base. The second effort conducted under this five year program involved the testing of restoration and revegetation methods and procedures on a heavily disturbed tank trail and began in 1996. Overall survival of transplanted shrubs at the tank trail was 72%. Survival in the four initial gravity fed planting areas was 68%. Survival was not significantly different between the emitters (74%) and the capsules (62%). Survival in the mesquite mounds was 64%, with no significant difference in survival between the ripped south section (58%) and the non-ripped North section (69%). The gravity feed system with nine 55 gallon containers had a survival rate of 76%. The perforated pipe section had a survival rate of 86%. A comparison between the perforated pipe and 55 gallon container irrigation methods demonstrated a significantly lower survival rate for the 55 gallon container irrigation system. In the seeded area, a significantly higher percent coverage of non-seeded native species occurred in the ripped areas. There was a significantly higher number and percent coverage of seeded native plants in the imprinted plots compared to both the pitted and control plots. There was also a significantly lower number of nonnative species in the imprinted plots than in the control plots. In the non-mulch plots there was a higher percent cover of seeded native plants, a higher number of non-seeded natives and a higher number and percent coverage of nonnative plants. The results from the Tank Trail research confirm the use of ripping as an inexpensive method by which narrow, moderately disturbed areas, such as dirt roads and parking lots, also seen in the original VSTOL restoration project conducted in 1995-96. This method, combined with imprinting and direct seeding of large disturbed areas, shown to be practical during the Tank Trail project, can provide a low cost, efficient method of revegetating disturbed desert site within the Marine Corps Air Ground Combat Center. However, the low survival rates experienced during the first two years of the Tank Trail project compared to the extremely high survival rates of the initial VSTOL project, highlight the impact and importance of the El Nino phenomenon to desert restoration.

INTRODUCTION

This is the final report for the Plant Community Restoration project at Twenty-nine Palms Marine Corps Air Ground Combat Center (MCAGCC) near Twenty-nine Palms, California. The project, which began in early 1995, was initiated by the National Resources and Environmental Affairs Directorate (NREA) at the MCAGCC as an effort to develop and test methods of native plant revegetation in disturbed areas while simultaneously controlling erosion and dust. The first effort was undertaken from February 1995 through June 1996 and involved the testing of restoration methods and procedures at the Vertical Short Take-off and Landing site located in the Sand Hill region of the Base. A complete report on the results and conclusions of this effort was previously submitted under the title "Plant Community Restoration Marine Corps Air Ground Combat Center, Twenty-nine Palms", dated 20 June 1996. The initial efforts covered under this earlier report will not be duplicated in this report, though the Discussion Section in this report will integrate the earlier findings where applicable.

The second effort conducted under this five year program involved the testing of restoration and revegetation methods and procedures on a heavily disturbed tank trail and began in 1996. This tank trail, running parallel and west of Del Valle Road, just to the north of the Berkeley Avenue turnoff, had become unnecessarily wide and was increasingly encroaching on adjacent undisturbed creosote bush scrub habitat. The tank trail was divided in half lengthwise, and the western half, adjacent to the undisturbed vegetation, became the project site. The eastern half of the tank trail remains active and is visually and physically separated from the site by a railroad tie barrier. The site is approximately 1600 meters long by 50 meters wide, running roughly north to south.

STUDY AREA

The tank trail site was divided into two units. Unit one, roughly the southern half of the site, was installed between March 1996 and January 1998 (Figure 1). Unit two, the northern section of the site, was installed in October 1997 (Figure 2). The Tank Trail site is located alongside an area that is dominated by creosotebush (Larrea tridentata) and white bursage (Ambrosia dumosa), typical Mojave Desert scrub habitat. The entire length of the Tank Trails slopes slightly to the south and, though the less disturbed area south of the Tank Trail site has a fairly loose, sandy substrate, the site itself suffers from extreme compaction with a top layer (2-10 cm deep) of extremely fine dust caused by the weight of both wheeled and track vehicles over many years of use.

FIGURE 1

Figure 2

In addition to the tank trail site, a nitrogen mulch interaction study was undertaken and funded by the Soil Ecology and Restoration Group (SERG) in March 1998. This study site was located at the Vertical Short Takeoff and Landing area (VSTOL) of MCAGCC, near the Sand Hill area of the base. This site is on an abandoned landing strip with runways and aircraft parking areas treated with Soil Sement, which forms a hard concrete-like surface. As part of an effort to revegetate this area, SERG designed an experiment on a portion of the main runway. The habitat surrounding the VSTOL site is typical Mojave Desert scrub, with both creosotebush and bursage dominating the vegetation. As with the Tank Trail site, the area adjacent to the restoration site has a fairly loose, sandy substrate while the site itself suffers from extreme compaction thorough both the impact of wheeled vehicles and aircraft and the use, as described above, of Soil Sement to help build the aircraft runway and taxi areas.

MATERIALS, METHODS AND HISTORY

Unit One

During March 1996, twelve 110 meter by 13 meter treatment quadrats were setup in section one. To investigate different soil preparation techniques, six of the experimental quadrats were ripped to reduce soil compaction. Since both imprinting and pitting can also reduce surface compaction, six of the experimental quadrats were not ripped. In each group of six, two quadrats were imprinted, two were pitted and two left untreated to serve as controls. Once the soil preparations were complete, half of each treated area was seeded via hand broadcasting with the following native seed mix: Larrea tridentata (12 lbs.), Ambrosia dumosa (5 lbs.), Sphaeralcea ambigua (4 lbs.), Achnatherum hymenoides (15 lbs.) and Croton californica (2 lbs.).

In addition to seeding, mulch was randomly applied to the experimental quadrats. Each seeded area received bark mulch treatment over approximately half of the section. Treatment included emptying twenty-five 2 cubic foot bags of medium sized decorative bark in random spots, spread out to provide a cover layer approximately 2-4 cm in depth. It was anticipated that these spots would enhance seed germination, catch organic matter and increase water retention, thereby creating islands of fertility.

In order to measure the success of the seeded plots and to determine the relative effectiveness of the soil preparation techniques and amendments in promoting both seeded and natural revegetation, germination data was collected in the nine unplanted soil treatment plots. Within each plot, ten randomly located one meter square quadrats were established, and all plants present were recorded by species, number and estimated percent coverage of the quadrat. Twenty quadrats were recorded within each of the three plots containing areas of added bark mulch; ten within barked areas and ten without bark. The plants recorded were categorized as seeded natives, non-seeded natives and non-natives. Analysis of Variance (ANOVA) was performed to compare ripped and non-ripped plots, seeded and non-seeded plots, and to do a three way comparison between imprinted, pitted, and control plots. The mulched quadrats within plots 2, 6 and 10 were compared with non-mulched quadrats from the same three plots.

In the six ripped experimental quadrats, three were planted with 381 plants (88 Larrea tridentata and 44 Ambrosia dumosa in each quadrat). In the unripped quadrats, only 19 plants were planted because severe soil compaction interfered with excavation of the planting holes. At the time of planting all seedlings received approximately one liter of water and a protective device in the form of either a treepee or tubex. These plantings were watered from March 1996 to October 1996 by hand at two week intervals using approximately one liter of water placed in each protective shelter.

Since the conventional watering regime yielded an average survival of only 13% for the 1996 plantings, replanting was necessary to meet the contract minimum requirement of 60% plant survival. Replanting was conducted in March and April 1997. An experiment was setup with these replants. Fifty island groupings containing four plants each were set out in three experimental treatments. These treatments included flood irrigation into a watering basin, flood irrigation into a watering basin lined with a layer of punched straw mulch (to improve water penetration and reduce surface evaporation), and diffusion irrigation using porous ceramic capsules. In this third treatment low fired, high porosity, ceramic irrigation capsules were created specifically for this project. There are no commercial sources for these capsules and they are being researched and developed by SERG. Figure 3 shows the ceramic capsules attached to a 5 gallon reservoir. All three treatments receive the same amount of water, five gallons, to compare slow irrigation through the ceramic capsules to surface watering.

In January 1998, to ensure the minimum survival requirement was met, the southern or island area of the tank trail site was replanted with 100 plants. For the replanted shrubs the supplemental irrigation methods were abandoned and replaced with shallow basins (Figure 3). The different irrigation methods which had been applied to these plants at the original replanting in March and April 1997 were disregarded statistically as they had become irrelevant over time due to the loss of straw mulch to wind and because the five-gallon reservoir systems had proven ineffective in the long term due to a lack of durability and a tendency to become clogged.

Twenty-four mesquite mounds were constructed by military personnel and equipment in February 1996 using on-site sand. These mounds are approximately 6 feet high and 12-15 feet in length. Formation was supervised by SERG personnel. The completed mesquite mounds also serve as windbreaks. This disruption to laminar wind patterns reduces wind erosion, increases soil fertility and provides wildlife habitat. The mounds also serve as a natural but highly visible means to mark the edge of the tank highway, further enhancing the effect of the railroad ties.

 

Figure 3. Installation of Unit One basin plantings. A) Five gallon bucket with ceramic capsules B) Planting Basins

Four groups of three mounds were constructed on a non-ripped section of the trail and four groups of three on a ripped section. Six mesquite seedlings (Prosopis glandulosa) were planted on each mound and given approximately one liter of water. All seedlings were provided with protective devices in the form of tubex tree shelters to prevent herbivory. Watering was carried out in the same manner as described earlier (Figure 4).

Since survivorship on the mesquite mounds was below contract requirements of 60% after three months, this area was also replanted. In December 1996 and January of 1997 seventy-two (72) mesquite seedlings were added to the surviving 25 mesquite plants bringing the total number of live mesquite on each mound to four. At the time of planting each seedling received two cartons of Driwater placed in contact with the root zone and a large volume deep pipe to facilitate and improve the effectiveness of future watering. Driwater is a commercial product containing water chemically bound in a cellulose-alum matrix that is slowly degraded by naturally occurring soil microbes. Driwater was used in this case to reduce transplant shock and bolster seedling survival during establishment.

Due to continued low survivorship, the mesquite mounds were again replanted in November 1997 with approximately 25 plants. Each plant was provided with a four inch wide deep pipe as was done previously on the mesquite mounds. Unlike the original plantings, Driwater was not used as we suspected it did not allow for optimal water dispersal, thus confining the growing roots to an inadequately small area of temporarily available moisture.

In January 1998 a small area within the mesquite mounds was utilized to compare the survival of three native species which were germinated in the SERG greenhouse, each with and without native mycorrhizal inoculum. Species used were Hymenoclea salsola, Atriplex canescens and Encelia farinosa for a total of 59 plants (Figure 4). Chi-square analysis was conducted to compare survival of each species between inoculated and non-inoculated plants.

In May 1997, four 55 gallon barrels and gravity feed irrigation systems each supplying 25 plants were installed on hummocks. Two barrels were fitted with standard, commercially available, adjustable drip irrigation fittings and two barrels were fitted with diffusion type ceramic capsules (Figure 5). A comparison of the two different water delivery systems was conducted to estimate differences in irrigation efficiency, an important variable in estimating

 

Figure 4. Installation of Unit One mycorrhizae plot and mesquite mounds. A) Mesquite mounds and B) Mycorrhizae study plot.

Figure 5. Installation of Unit One gravity feed system. A) Commercially available emitter B) Custom made ceramic capsule.

the quantity of water necessary to maintain plant survival. To help ensure survival the quantity of water delivered to each plant was 2 gallons per watering event.

The gravity feed area in unit one, consisting of four 55 gallon containers, was not replanted or altered in any way since it was established in May 1997. ANOVA was used to compare survival between emitter-fed plants and capsule-fed plants.

Unit Two

Unit two was planted in October 1997, using a variety of irrigation methods and a total of 615 plants. Starting from the northern boundary of Unit one, the initial planting was a series of nine 55 gallon containers, each of which supplied 24 plants with water, 8 plants on each of three sections of irrigation tubing extending from the bottom of each container (Figure 6). Each section of tubing was branched into eight outlets, each terminated in a ceramic capsule which was buried near the root zone of each plant. The containers were arranged to provide water to each capsule through gravity-induced pressure. The intent was to provide water as efficiently and in a timely fashion, with the ceramic capsules releasing water through diffusion at a rate dependent on the aridity of the surrounding soil. While the irrigation tubing was standard commercially-available material, the cartridges were manufactured by SERG using a standard bottle mold. The 55 gallon containers were placed close enough to the active tank trail to allow easy access by commercial water truck.

In the next section a total of 316 plants were planted using three inch diameter flexible perforated plastic pipe as the water delivery medium. Fifteen 100 foot long sections of pipe were buried in ten inch deep trenches with approximately 20 plants placed along each side of each pipe (Figure 7). Both ends of the pipe were elevated so that the pipe would hold water and release it through the perforations. The intent was to experiment with providing water below ground where it would be both needed and less susceptible to evaporation. These pipes were placed with one end adjacent to the active tank trail for ease of filling by a water truck.

In a natural basin area close to the southern end of Unit 2, ten Chilopsis linearis (Desert willow) were planted without supplemental irrigation equipment. This is a wash inhabiting species that tends to do relatively well in low-lying areas which collect water. In an

Figure 6. Installation of Unit Two gravity feed devices. Each reservoir serves 24. A) A completed system prior to planting and B) A system several months after planting.

Figure 7. Installation of two perforated pipe plantings. A) One of the fifteen pipe sections just after planting and B) A pipe being filled from the active area of the tank trail.

extension of this idea, a group of catchments, roughly four meters square, were created near the center of Unit 2 (Figure 8). Each catchment consisted of two berms forming a water collection point at the low corner of each catchment, each with three or four plants for a total of 32 plants. These were not only connected but progressively lower in elevation as they moved further from the tank trail, creating a terraced effect. This terracing would allow a water truck operator to fill all of them from one spot on the active tank trail.

The last planting in Unit 2 consisted of 91 plants with a variety of irrigation devices, including 4 inch wide deep pipes with 64 ounce ceramic capsules attached to the bottom, 2 inch wide deep pipes with 32 ounce ceramic capsules attached to the bottom and 4 inch wide deep pipes (Figure 9). These were planted one meter apart from each other in a square.

All tank trail plants were watered by a contracted water truck or, when necessary, by hand by SERG personnel. With few exceptions, the watering regime was every three weeks, never exceeding one month between watering except during the wet season (November through March).

After the last survival recording in March 1999, chi-square analysis was performed to compare survival in the largest irrigation treatments, the perforated pipe plantings and the nine gravity feed systems, both of which were installed in October 1997.

Vertical Short Take-off and Landing (VSTOL) Site Nitrogen Study

As part of an effort to develop revegetation procedures for the VSTOL runway, SERG designed an experiment on a portion of the main runway (Figures 10 and 11) which had been ripped to a depth of 3 feet by base personnel and equipment. This experiment consisted of three identical 10 meter square plots, each containing four soil treatments; alfalfa straw mulch, wheat straw mulch, sawdust mulch and a control. In addition, half of each plot was fertilized with Ammonium nitrate. This effectively created eight sub-plots, with each plot having four soil treatments, each of which had fertilized and non-fertilized sections. Within each of these eight subplots, four Ambrosia dumosa were planted. In addition, each sub-plot was seeded over a one meter square area with both native and exotic seeds.

Figure 8. Installation of Unit Two catchments. Catchments had just been watered.

Figure 9. Installation of Unit Two individual watering mechanisms. A) Thirty-two ounce ceramic capsules with 2 inch deep pipe and B) Sixty-four ounce ceramic capsule with 4 inch deep pipe.

Figure 11. Installation of VSTOL Site. A) Spreading out organic mulches and B) Completed plot.

The different mulch materials represent a gradient in carbon:nitrogen ratios. Hypotheses to be tested included the possibility that a particular C:N ratio will prove to be significantly more effective in promoting the development of microorganisms, subsequently lowering the amount of available soil nitrogen. The fertilizer is intended to simulate the atmospheric nitrogen deposition which occurs in polluted areas. The main hypothesis being explored is that the additional nitrogen provided by atmospheric deposition in polluted areas creates

an advantage for exotic species, which are able to utilize an overabundance of nitrogen more effectively then native plants, which have a more limited capacity for nitrogen usage having evolved under low-nutrient conditions.

The data collected included soil nitrogen levels at above and below ground levels. Nitrate and ammonium levels were measured in each subplot, using ion-exchange resin bags. Survival and height of the out-plantings were measured, and germination in the seeded plots quantified. These data were recorded beginning in May 1998, and collected on a bimonthly basis through January 1999.

 

RESULTS

The success rates for all research projects were above 60%, the minimum acceptable success criteria set by the Letter of Agreement. The original timeline was altered with an extension of one year due to the extremely low survival rates experienced during the La Nina winter of 1996-97 that resulted in well below average precipitation. The possibility of an extension being required if success criteria were not met had been addressed in the original Letter of Agreement and was agreed upon by both the Government and Agreement representatives.

Unit One

Final survival percentages for Unit one are recorded in Table 1 represent plants counted on 9 March 1999. Overall survival in the island plantings was 63%. Photographs are shown in Figure 12. Survival in the four initial gravity fed planting areas, planted in May 1997, was 68%. Survival was not significantly different (p >= 0.05) between the emitters (74%) and the capsules (62%). Survival in the mesquite mounds was 64%, with no significant difference (p >= 0.05) in survival between the ripped south section (58%) and the non-ripped North section (69%). A photograph is shown in Figure 13. Forty of the original 59 plants in the mycorrhizal study survived, for an overall rate of 68% survival (Table 2). There was

Table 1. Twenty-nine Palms Revegetation Overall Survival 3/9/1999

 

Planted

Alive

Survival

Unit One

Islands

400

250

63%

Mesquite

mounds

144

92

64%

Initial

Barrels

100

68

68%

Mycorrhizal

Experiment

59

40

68%

Unit two

Second Barrels

206

157

76%

Chiopsis

group

316

272

86%

Perforated

Pipe

316

272

86%

Catchments

32

32

100%

Treatment

Comparison

91

62

68%

TOTALS

1,358

980

72%

 

 

Figure 12. Unit One Basins. A) Cylindrical plant shaped by Tubex and B) A successful basin planting result.

Figure 13. Unit One mesquite mound.

Table 2. Mycorrhizae study plot.

Species

Mycorrhizae

Percent Survival

Standard Error

Hymenoclea

Yes

90

0.10

Hymenoclea

No

90

0.10

Encelia farinosa

Yes

70

0.15

Encelia farinosa

No

78

0.15

Atriplex polycarpa

Yes

40

0.16

Atriplex polycarpa

No

50

0.17

 

no significance in the survivorship (p = 0.64) between the inoculated (67%) and non- inoculated (72%) plants. A photograph is shown in Figure 14. No survival data was taken for the seeded soil treatment plots in March 1999, however, germination data was collected in February 1998 in the nine unplanted soil treatment plots (Table 3). ANOVA performed on the soil treatment plots taken from the January 1998

monitoring revealed a significantly higher percent coverage of non-seeded native species in the ripped areas than in the non-ripped plots, with P = 0.03 (Figure 15). There was a significantly higher number and percent coverage of seeded native plants in the imprinted plots compared to both the pitted and control plots, with P = 0.0001 for number and

P = 0.0008 for percent coverage (Figure 16). There was also a significantly lower number of nonnative species in the imprinted plots than in the control plots, with P = 0.003 (Figure 17).

Several significant differences were found between the plots with added bark mulch and those without mulch (Figure 14). These included a higher percent cover of seeded native plants in the non-mulch plots (P = 0.004); a higher number of non-seeded natives in the non-mulch plots (P = 0.006); and a higher number (P = 0.0001) and percent coverage (P = 0.0001) of nonnative plants in the non-mulched plots (Figure 18).

 

Figure 14. Unit One bark plots and micorrhizae plot. A) Bark plots and B) Mycorrhizae Plot.

Table 3. Twenty-nine Palms Germination Study Plant List 2/19/1998

 

Native, Seeded

Native, Non-seeded

Nonnative, Non-seeded

Ambrosia dumosa

Abronia villosa

Brassica sp.

Larrea tridentata

Ambrosia acanthicarpa

Erodium sp.

Sphaeralcea ambigua

Astragalus sp.

Salsola tragus

 

Camissonia claviformis

Schismus barbatus

 

Cryptantha sp.

 

 

Dalea mollissima

 

 

Hymenoclea salsola

 

 

Lepidium nitidum

 

 

Malocothrix glabrata

 

 

Oenothera deltoides

 

 

Palafoxia arida

 

 

Pectocaryia platycarpa

 

 

Plantago insularis

 

 

Rafinesquia neomexicana

 

 

Unit Two

Final survival percentages for Unit two recorded in Table 1 represent plants counted on 9 March 1999. The gravity feed system with nine 55 gallon containers had a survival rate of 76%, with 157 out of 206 plants surviving. Seven of the ten Chilopsis plants planted together in the basin area survived for a survival rate of 70%. Photographs are shown in Figure 19. The perforated pipe section had 272 plants survive out of an original 316, leading to a survival rate of 86%. Photographs are shown in Figure 20. A comparison between the perforated pipe and 55 gallon container irrigation methods via Chi-square analysis demonstrated a significantly lower survival rate for the 55 gallon container irrigation system (P 0.05). All of the 32 catchment plants survived and 68% of the group of plants with various individual watering mechanisms survived (Figure 21). There was no significant difference of survivorship (p 0.05) between each of the individual watering mechanism treatments (Table 4).

Table 4. Individual watering mechanisms.

 

Treatment

Percent survival

Standard Error

4 inch deep pipe

81

0.10

32 oz. ceramic capsule

78

0.15

4 inch deep pipe + 64 oz. ceramic capsule

71

0.13

2 inch deep pipe + 32 oz. ceramic capsule

67

0.12

 

Figure 19. Unit Two Chilopsis basin and gravity feed devices. A) Gravity feed devices and B) Chilopsis feed devices.

Figure 20. Unit Two perforated pipe plantings. A) Overview of area and B) View of one irrigation line.

Figure 21. Unit Two individual irrigation mechanisms and catchments. A) Catchments and B) Individual watering mechanisms.

Vertical Short Take-off and Landing (VSTOL) Site Nitrogen Study

Ten months after planting, overall survivorship of Ambrosia dumosa at the VSTOL site was 78 percent. ANOVA statistical analysis was used to determine if the addition of organic amendments in combination with ammonium nitrate fertilizers had an affect on various dependent variables (Table 5). Results show that soil treatments had no significant effect on plant survivorship (p = 0.28), height (p = 0.22), NO3 (p = 0.10) or percent moisture (p = 0.98). Soil treatments did have a significant effect on the other dependent variables: higher NH4 in the alfalfa plots (p = 0.03); higher percent organic matter in the soil amended plots (p = 0.03); and higher pH in the control plots (p = 0.03). With the exception of one Isomeris arborea, no seedlings were observed growing in the seeded areas. Photographs are shown in Figure 22.

Table 5. Results from the VSTOL site ten months after installation.

 

Treatment

Percent survival

Height (cm)

NH4 (ug/ml)

NO3 (ug/ml)

Percent organic matter

pH

Percent moisture

 

 

 

 

 

 

 

 

Wheat unfertilized

50

25.2

17.0

2.6

1.4

7.5

1.1

Sawdust unfertilized

92

27.5

2.8

1.6

1.3

7.7

1.0

Control unfertilized

75

25.9

10.8

2.5

1.0

7.8

0.9

Alfalfa unfertilized

92

38.0

138.5

57.6

1.6

7.6

1.0

Wheat fertilized

75

18.7

18.5

6.0

1.5

7.7

0.9

Sawdust fertilized

83

31.6

20.4

5.7

1.6

7.9

0.9

Control fertilized

83

29.3

20.8

15.7

1.0

8.1

1.2

Alfalfa fertilized

75

27.7

376.7

30.2

1.6

7.6

1.2

Average

78

26.6

75.7

15.2

1.4

7.8

1.0

P-value

0.28

0.22

0.03

0.10

0.03

0.03

0.98

 

DISCUSSION

Unit One

Initially, irrigation for container plantings consisted of biweekly hand application of 1 to 2 quarts of water from 2.5 gallon watering cans into protective shelters surrounding each plant. This method was used to maintain the 1996 plantings and yielded an average survival of only 13 percent. This quantity of water proved to be insufficient. As a result of the low survivorship, a more efficient means of supplying water directly to the roots was necessary. Consequently, another experiment consisting of 229 island replants were set out in three different treatments comparing diffusion irrigation (with high porosity ceramic irrigation capsules), and flood irrigation into watering basins with and without straw mulch. Based on previous studies, the ceramic irrigation capsules would have a higher efficiency because the water is discharged directly into the root zone where it is needed and not on the surface where evaporation can take place.

For the replanted shrubs of January 1998, the supplemental irrigation methods were abandoned and replaced with shallow basins. The different irrigation methods which were applied to these plants at the original replanting in March and April 1997 were disregarded statistically as they had become irrelevant over time due to the loss of straw mulch to wind and because the five-gallon reservoir systems proved ineffective over the long term due to a lack of durability and a tendency to become clogged. The basins, which were constructed during the two replantings, were relatively successful, but required large amounts of water when irrigated and may have been too small to trap significant amounts of windblown seed and organic detritus to initiate additional plant colonization. At the time of final monitoring, overall survival in the island plantings was 63%. These results were 50% higher than the initial 1996 planting results, which had no basins involved. Even though techniques concerning the use of watering devices and mulches are in need of refinement, the use of basins alone, and their ability to trap more water applied to the soil surface, increased survivorship substantially. In remote areas, away from normal sources of irrigation water, basins could be used to passively collect rainwater and increase the survivorship of transplanted shrubs. Furthermore, no cleanup of irrigation materials is required when using this method.

The second irrigation system, consisting of 55 gallon drums that fed 25 plants each, had a survival rate of 64% in March 1999. Although not statistically significant, the use of commercial emitters produced a higher plant survivorship than the ceramic capsules. There were also less mechanical failures involved with commercial emitters, as the ceramic capsules tended to separate from the one-half inch polyethylene tubing. Due to water leakage resulting from component breakdown, the 55 gallon drum gravity feed system used more water than intended and required periodic adjustments post-planting. Despite its problems, this water delivery system may still be considered effective if located in areas that are near a water source and easily accessible for accomplishing required maintenance. To further complicate the results, these shrubs were planted in May 1997, when the weather had already become quite hot and dry; however, the plants which survived the initial transplant shock and the ensuing summer weather have survived and are healthy.

Final survivorship for shrubs growing on the mesquite mounds was 64%. Starting with the initial planting, providing the mesquite plants with enough water proved to be problematic. While hand watering the mesquite mounds during 1996 it was noticed that irrigation water occasionally eroded through the base of the tree shelters and washed down the face of the mound, reducing irrigation efficiency. This hand watering technique produced survival rates of only 17%. To improve irrigation efficiency and seedling survival, large volume deep irrigation pipes were installed on the mesquite mounds in 1997. These pipes were inserted to a depth of 18 inches and delivered up to 2 gallons of water directly into the root zone, helping to create a reservoir of water within the mounds to sustain seedlings during the hot summer months. Even with disappointing survival of the 1997 replants, probably due to the small size of the transplants and lack of spring precipitation, some of the mesquite seedlings grew rapidly. This suggests that the roots of some seedlings may have only now reached the reservoir of water created by deep pipe irrigation.

In early January 1997, Driwater was placed in direct contact with the root ball of 75 replanted mesquite seedlings. In theory, Driwater should help prevent transplant shock and give seedlings a head start on the growing season. However, expected results proved less than favorable. Two lessons were learned from this trial. First, Driwater at Twenty-nine Palms is subject to damage and loss due to coyote and rabbit disturbance. At a cost of $1.50 per carton, any future installations of Driwater at Twenty-nine Palms must be protected either by an olfactory repellent or physical barrier, such as poultry wire, to prevent costly losses. Second, Driwater appears to reduce initial watering requirements; however, this reduction in watering may not benefit long-term survival. After receiving only two supplemental waterings and virtually no significant precipitation, mesquite seedlings planted in late December 1996 and early January 1997 had a survival rate of 80% in April 1997. It was noted that mesquite seedlings from which the Driwater had been removed or disturbed by animal activity appeared to suffer higher mortality.

These results suggest that Driwater is effective in easing transplant shock in young seedlings and can be recommended for use during winter and early spring in low rainfall years. However, data from one of our sites in the Colorado desert suggests that use during summer planting may actually result in lower survival because of its tendency to reduce lateral root growth. This may have occurred with the mesquite mound plantings. Application of Driwater may have encouraged the development of local roots and reduced the development of deep roots into the reservoir of water created by deep pipe irrigation. It is therefore recommended that Driwater be used only during fall plantings just prior to winter rains and that it be used only as a way to help seedlings become initially established and not as a long term irrigation method.

The mesquite mounds have been slow to develop. The primary reason for this problem is believed to be the unfortunate timing of the construction and planting of the mounds. The first group of mesquite seedlings were planted during the La Nina season of 1996-97, with little subsequent rainfall. This not only led to a large die-off of seedlings, but little growth of those that survived. Only during the wet 1997-98 winter season was any growth noted. Those seedlings that have survived and demonstrated acceptable growth rates have been those with deep pipe irrigation systems. Driwater and surface irrigation has not been that successful on the mesquite mounds. The use of deep pipes are highly recommended as a long term irrigation method for group planting projects such as mesquite mounds.

No significant difference in seedling survival occurred between the mesquite mounds in the ripped south section (58%) and those in the non-ripped north section (69%). However, because the mounds were easier to build in the ripped section because of the abundance of loose soil, if a large number of mounds are planned, it is recommended that the area be ripped prior to construction.

Forty of the original 59 plants in the mycorrhizal study survived for an overall survival rate of 68%. At final monitoring, no significance was noted in the survivorship between inoculated (67%) and non-innoculated (72%) Atriplex canescens. For the previous monitoring, taken in July 1998, non-innoculated plants had a significantly higher survivorship than inoculated plants. Atriplex canescens is a member of the non-mycorrhizal plant family Chenopodiaceae, the added fungal matter in the inoculum may actually had a pathogenic effect, though such a determination is beyond the scope of this project. Increased survival rates of transplanted shrubs as a result of mycorrhizal inoculum addition mat be species specific. Further research should be conducted to determine which if any, desert species benefit from the addition of mycorrhizae.

The higher percent coverage of non-seeded natives in ripped plots compared to non-ripped plots was the result of seedlings being larger in size. Larger plants probably developed on ripped plots due to their enhanced ability to retain water and windblown detritus and, with the reduced soil strength found in the mechanically ripped plots, seedling roots were better able to spread through the soil in an effort to acquire both water and nutrients. The similarity in number of found on both ripped and non-ripped plots probably occurred because optimal germination was restricted to the lowest points in each plot. Thus, both types of plot contained roughly the same number of germinations, but ripped plots were able to support significantly larger plants. It is also possible that since many of the non-seeded natives were fast growing annuals, an individual plant in a physically favorable location may have grown quickly enough to out-compete other nearby plants, thereby reducing the total number of plants in each of the ripped plots.

A similar situation may have existed in imprinted plots, which produced both higher numbers and percent cover of seeded natives then either pitted or control plots. Imprinting creates a regular pattern of numerous small indentations. These impressions may have provided more suitable germination conditions than pitting, which tends to create an irregular pattern of fewer and larger indentations. The fact that non-seeded natives were not in greater abundance in the imprinted plots is possibly an indication that such shallow indentations are not particularly effective in trapping windblown seed, although they were able to retain seeds deposited there by hand.

Though there was no significant difference in density of seedlings, for either from hand-seeding or natural recruitment, between the ripped and non-ripped sections, it is still recommended that heavily compacted areas be ripped prior to seeding. Ripping appears to enhance the growth of seedlings. On the other hand, imprinting appears to reduce the growth of nonnative seedlings, but apparently does not provide an effective surface for capturing wind-blown native seeds from a nearby undisturbed site. Possibly a combination of ripping and imprinting, especially for large disturbed areas, might provide the best environment for taking advantage of the local seed bank while reducing the impact of invasive exotic species such as annual grasses.

 

Unit Two

The shrubs in this unit were planted in October 1997, which proved to be extremely favorable due to the El Nino phenomenon which occurred. The area received abundant rainfall and, after initial watering, it was unnecessary to irrigate until April 1998.

Seven of the ten Chilopsis plants survived, most probably due to the moisture holding capacity of the natural basin they were planted in. Although sampling size was small and no statistical analysis can be applied, the successful rate of survivorship reiterates the fact that location of a species habitat is important to consider when planting shrubs. If Chilopsis were planted on a flat plain, survivorship would probably have been much lower.

The gravity fed plantings had a survivorship of 76 percent. The survival rate might have been higher if not for the numerous leaks which developed in the system. As with the gravity fed systems in Unit one, the connection between the ends of the irrigation tubing and the ceramic capsule were weak, and leaks developed on nearly all nine containers each time the system was used. Unfortunately, leaks occurring at the connection between the tubing and the 55 gallon drums were capable of draining an entire reservoir, leaving all 24 plants without water. Efforts to do field repairs ultimately proved ineffective, and all affected plants were individually watered starting in June 1998.

The perforated pipe group had a significantly higher survival rate (86%) than the nine gravity fed plantings (76%). The use of perforated pipe as a method to deliver water to native seedlings appears to be the most efficient and least expensive irrigation procedure tested so far. The perforated pipe system was comparatively trouble-free and may be the most efficient system of all methods tested for delivering water quickly to a large number of plants. A disadvantage of this technique is the difficulty encountered when removing the pipe once shrub establishment has been achieved.

The catchment plantings were successful, although they were too few in number to compare statistically with other plantings. All 32 plants survived, probably due to the large quantity of water used to irrigate them. This, however, is also the major drawback to the large-scale application of this technique. Unless significant quantities of water are readily available, this system would probably not be economical.

The 91 plants which were planted together with various individual watering devices had a survival rate of 68%. No significant effects were found between the different irrigation devices. This may be due to the fact that during watering events, not only was water place in the irrigation devices, but also around the plant, thus negating the effects of the irrigation devices. In general, deep pipes may be most effective for use in areas where the ground is not flat, such as on mesquite mounds.

Vertical Short Take-off and Landing (VSTOL) Site Nitrogen Study

Ten months after planting, overall survivorship of Ambrosia dumosa at the VSTOL site was 78 percent. Results show that the soil treatments had no significant effect on plant survivorship (p = 0.28), height (p = 0.22), NO3 (p = 0.10) or percent moisture

(p = 0.98). Similar to the Tank Trail Unit one experiment, the addition of organic amendments did not improve either the success of survivorship of transplanted shrubs or the germination rates in the seeded areas. With the exception of one Isomeris arborea, no seedlings were observed growing in the seeded areas. Since these results were duplicated at the tank trail project, it raises the question as to whether or not the addition of organic amendments has any practical value in the field.

The soil treatments did have a significant effect on NH4 (p = 0.03), percent organic matter (p = 0.03) and pH (p = 0.03). The higher levels of ammonia can be attributed to the addition of fertilizer. Not surprisingly, in every case, the fertilized plots had a higher amount of ammonia. Ammonia bonds with anions present in the soil and is then broken down into nitrates by nitrifying bacteria. If a large amount of nitrifying bacteria were present in the soil, then we would expect to see a larger amount of nitrates in the soil, but this was not the case. This suggests that the desert microorganisms necessary for mineralization of mulch are probably missing from disturbed soils. It could have been that the nitrates, being in short supply, were quickly used up by the existing vegetation, but this is unlikely because the soil samples were taken at a distance outside the reach of nearby plant roots.

Percent organic matter was highest in the alfalfa plots, but had no affect on plant survival. The pH was highest in the control plots and the fertilized plots. Generally, the more disturbed a site is, the more alkaline the soil becomes and the less nitrogen and organic matter are present in the soil. Whereas the organic amendments helped to lower the pH, the reasons for the raised pH in the fertilized plots cannot be explained at this time. Overall, the affects on plant survivorship were negligible.

A similar experiment with the addition of straw and bark mulch was performed at the Army's National Training Center in Fort Irwin, California. The mulches were added to catchments and, after one year, survivorship of transplanted shrubs was significantly higher in the straw and bark treatments than in catchments which received no organic amendments. Such varying results suggest that mulch may only have value in certain situations. Apparently, it is most effective when there is an abundance of water. If this requirement is not met, then mulch may wick away the moisture from the plants and cause more harm than good. More research into the use of mulch as a restoration procedure is required before its use or non-use is recommended.

CONCLUSIONS

Unit One

Results from the Tank Trail experiments have demonstrated the benefits of ripping a compacted area to enhance its ability to revegetate. By reducing the soil strength through ripping, both water infiltration and soil mineralization increases along with a plant's ability to move its roots through the soil. The end results of such actions are larger seedlings and increased coverage when compared to a non-ripped area. The speed of a restoration effort is increased through the physical effect of ripping the soil, even if no other actions are completed, since volunteer seedlings that become established from wind blown seeds will flourish in such an enhanced environment. It is highly recommended that any site suffering from heavy compaction, such as the Tank Trail, be thoroughly ripped prior to any other restoration activity being conducted. In certain situations, such as heavily used but narrow roadways, ripping may be all that is required, with volunteer seedlings becoming established on the site from adjacent undisturbed areas serving as native seed sources. For an inexpensive and efficient method to revegetate the numerous old and unused roads found throughout the Base, ripping is therefore the recommended procedure to use.

Tank Trail results also seem to indicate that imprinting a large area in preparation for direct seeding can greatly improve both initial germination and overall success. The Tank Trail seeded/imprinted areas demonstrated both higher numbers and greater coverage of native species than either control or pitted plots. The shallow depressions formed by the imprinter can apparently enhance a direct seeding effort, but do not seem to aid in the establishment of native volunteer seedlings. It is recommended that any future restoration effort at Twenty-nine Palms relying on direct seeding as the primary source of revegetation include imprinting as a site preparation method. If the imprinting and seeding effort can be timed to occur during a wet winter season, such as occurred in 1997-98, results should be excellent with a minimum of money and effort being expended.

Bark mulch plots demonstrated no advantages over non-bark plots, and actually had significantly fewer non-seeded natives, a lower percent cover of seeded natives and a lower number and percent coverage of non-natives. This may be due to the recalcitrant nature of the bark, which takes a minimum of three to five years to mineralize, and therefore has not yet released significant quantities of the desired nutrient and fungal amendments into the soil. Advantages to native shrubs provided by recalcitrant mulch being added to disturbed soil normally do not appear until a large amount of the mulch has decomposed and entered into the mineralization cycle. In the meantime, the bark may actually reduce seed germination by physically preventing seeds from germinating due to size and bulk of the bark. Though bark mulch may provide an improved environment for established seedlings, it appears to be detrimental to seeding efforts. It is recommended that the use of bark mulch be restricted to use with transplanting operations and not direct seeding.

Unit Two

The gravity feed irrigation system might be quite effective if the weak connections could be made stronger. The 55 gallon drums were quickly filled up with water by the contracted water truck and the slow release of that water to the soil would have been an ideal method of irrigation. Though ceramic capsules appear to have excellent possibilities, problems with loose fittings and system leaks have yet to be overcome. Continued research should be done on the use of ceramic capsule irrigation systems since they may yet prove to be a cost efficient irrigation method for desert restoration.

The one major fault of the perforated pipe irrigation system is its use of large quantities of water. This could possibly be reduced by using non-perforated pipe and manually drilling holes in the pipe adjacent to the plants. This would allow the pipe to fill faster due to the reduced number of outlets, and would direct the water to only where it was needed. It is recommended that for restoration efforts that allow a water source such as a water truck to be used, perforated pipe be selected as the means of irrigating the seedlings.

The use of catchments as an irrigation system for restoration efforts is recommended only for small scale projects. However, like basins, catchments might possibly be efficiently used in remote area restoration projects, without easy access to irrigation water, where the shrubs planted in the fall or early winter could take advantage of the captured rain. Such use needs to be tested, however, before it can be recommended for actual practice.

Overall, the contract requirement of 60% survival one year post-planting was met. The abundance of native annuals which germinated in the plots during the spring of 1998 was encouraging, as they will add to both the soil seed bank for future years and increase necessary nutrients to the soil needed establish a self-sustaining mineralization system to the project area.

Natural irrigation will always produce the best results, but it is infrequent and difficult to predict. During most years, some type of supplemental irrigation will be necessary to ensure plant survival. To summarize, based on our experiences, techniques and methods that we believe may prove useful for future restoration projects at Twenty-nine Palms include; the use of perforated pipes, deep pipes, flood irrigation and commercially available drip irrigation systems. Techniques which have proven to be ineffective or in need of refinement include; custom made ceramic irrigation emitters, gravity fed irrigation systems and Driwater.

 

Vertical Short Takeoff and Landing (VSTOL) Site Nitrogen Study

In theory, desert shrubs should benefit from increasing the carbon to nitrogen ratio by the addition of recalcitrant amendments such as bark or straw, but this was not the case. Also, the addition of mulches to the soil should increase soil moisture, allowing the shrubs to grow more successfully, but this was not the case either. Adding organic amendments to the soil also did not change the amount of nitrates (NO3), the ready-to-use form of nitrogen for plants. Though not statistically significant, alfalfa had the highest levels of nitrates in the soil. If raising the carbon to nitrogen ratio is the theoretical goal to improved native plant vigor, then using alfalfa mulch would be the least favorable option of the three. Wheat and saw dust had much lower counts of nitrates in the soil.

The results of the research on soil treatments did suggest that the addition of fertilizers on disturbed soils as a plant growth enhancer is impractical, and, although not apparent during this experiment will, in all probability, benefit nonnative plant species more than native plant species since nonnative plant species are better adapted to taking advantage of higher levels of nitrogen in the soil. It is therefore recommended that the addition of fertilizer to stimulate native plant growth not be done in connection with restoration projects at MCAGCC.

Overview

The results from the Tank Trail research confirm the use of ripping as an inexpensive method by which narrow, moderately disturbed areas, such as dirt roads and parking lots, can be revegetated that was seen in the original VSTOL restoration project conducted in 1995-96. This method, combined with imprinting and direct seeding of large disturbed areas that was shown to be practical during the Tank Trail project, can provide a low cost, efficient method of revegetating disturbed desert site within the Marine Corps Air Ground Combat Center. However, the low survival rates experienced during the first two years of the Tank Trail project compared to the extremely high survival rates of the initial VSTOL project, highlight the impact and importance of the El Nino phenomenon to desert restoration. If the low cost methods described above can be scheduled for completion during years that are predicted to experience an El Nino winter with its above average precipitation, then the survival rates will, in all probability, be well above acceptable minimums. If such efforts are accomplished during La Nina years, then survival rates will probably be below acceptable standards. Climatology has now reached the point where El Nino phenomena can be fairly accurately predicted, and such information should become as much a part of any restoration plan as a species listing.


Vertical Short Takeoff and Landing (VSTOL) Project Results

Tank Trail Project